Amir Tal

Fabrication and characterization of three-dimensional copper metallodielectric photonic crystals

Three-dimensional metallodielectric photonic crystals were created by fabricating a micron-scale polymeric template using multiphoton direct laser writing (DLW) in SU-8 and conformally and selectively coating the template with copper (Cu) via nanoparticle-nucleated electroless metallization. This process deposits a uniform metal coating, even deep within a lattice, because it is not directional like sputter-coating or evaporative deposition. Infrared reflectance spectra show that upon metallization the optical behavior transitions fully from a dielectric photonic crystal to that of a metal photonic crystal (MPC). After depositing 50 nm of Cu, the MPCs exhibit a strong plasmonic stop band having reflectance greater than 80% across the measured part of the band and reaching as high as 95% at some wavelengths. Numerical simulations match remarkably well with the experimental data and predict all dominant features observed in the reflectance measurements, showing that the MPCs are structurally well formed. These data show that the Cu-based process can be used to create high performance MPCs and devices that are difficult or impossible to fabricate by other means.

Rigorous electromagnetic analysis of volumetrically complex media using the slice absorption method

There is tremendous demand for numerical methods to perform rigorous analysis of devices that are both large scale and complex throughout their volume. This can arise when devices must be considered with realistic geometry or when they contain artificial materials such as photonic crystals, left-handed materials, nanoparticles, or other metamaterials. The slice absorption method (SAM) was developed to address this need. The method is fully numerical and able to break large problems down into small pieces, or slices, using matrix division or Gaussian elimination instead of eigensystem computations and scattering matrix manipulations. In these regards, the SAM is an attractive alternative to popular techniques like the finite-difference time domain method, rigorous coupled-wave analysis, and the transfer matrix method. To demonstrate the utility of the SAM and benchmark its accuracy, reflection was simulated for a photonic crystal fabricated in SU-8 by multiphoton direct laser writing. Realistic geometry was incorporated into the model by simulating the microfabrication process, which yielded simulation results that matched experimental measurements remarkably well.

Silvered three-dimensional polymeric photonic crystals having a large mid-infrared stop band

Interest in three-dimensional (3D) metal photonic crystals (MPCs) has grown considerably given their potential applications in optics and photonics. Yet, experimental studies of such materials remain few because of the difficulties associated with fabricating 3D micron- and sub-micron-scale metallic structures. We report a route to MPCs based on metallization of 3D polymeric photonic crystals fabricated by multi-photon direct laser writing. Polymeric photonic crystals (PCs) having simple-cubic symmetry with periodicities varying from 1.6 to 3.2 microns were created using a cross-linkable acrylate pre-polymer. The resulting dielectric PCs were metallized by electroless deposition of silver. Analysis of the metallized structures in cross-section by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy shows that silver deposited conformally onto the entire micro-porous lattice. The dielectric and metallized PCs were characterized by Fourier transform infrared (FTIR) spectroscopy in the (001) direction. The polymer photonic crystals exhibit a stop band resulting in circa 60% reflectance centered at 3.2 to 6.4 microns, depending upon the lattice period, with a full-width at half-maximum (FWHM) of 500 nm. Interestingly, FTIR spectra of the metallized PCs show widened stop bands of nearly 6 microns FWHM, while the center wavelengths were red shifted and ranged from 6 to 7 microns. The appreciable broadening of the stop band due to the presence of the deposited silver is a result consistent with previously reported theoretical and experimental data for all-metallic 3D PCs. Thus, the approach described here appears suitable for fabricating 3D MPCs of many symmetries and basis sets and provides a path for integrating such structures with other micron-scale optical elements.

Metallo-dielectric nanophotonic materials via direct laser writing and electroless metallization

Interest in three-dimensional (3D) metallo-dielectric photonic crystals (MDPCs) has grown considerably given their potential applications in optics and photonics. MDPCs can exhibit intriguing and potentially useful optical properties, including ultra-wide photonic bandgaps, engineered thermal emission, and negative refractive index. Yet experimental studies of such materials remain few because of the difficulties associated with fabricating 3D micron- and sub-micron-scale metallic structures. We report a route to MDPCs based on metallization of a 3D polymeric photonic crystal (PC) fabricated by multi-photon microfabrication (MPM). Polymeric PCs having face-centered tetragonal symmetry and micrometer-scale periodicity were created using a cross-linkable acrylate or epoxide pre-polymer. The resulting PCs were metallized by electroless deposition of silver or copper. Analysis of the metallized structures in cross-section by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy shows that silver deposited conformally onto the entire micro-porous lattice. The dielectric and metallized PCs were characterized by Fourier transform infrared (FTIR) spectroscopy. The polymer photonic crystals exhibit a stop band with strong reflectance near 4 to 6 microns, depending upon the lattice period. In contrast, FTIR spectra of the metallized PCs show widened stop bands of nearly 6 microns and greater and maximum reflectance exceeding 90%. The appreciable broadening of the stop band due to the presence of the deposited metal is a result consistent with previously reported theoretical and experimental data for all-metallic 3D PCs. Thus, the approach reported here appears suitable for fabricating 3D MDPCs of many symmetries and basis sets and provides a path for integrating such structures with other micron-scale optical elements.